"The colour purple is always calming," diversional therapist Sandra Rowan said.
When the sun starts to go down, from about 3pm onwards, is when they start using the room.
"When the sun goes down, so does their behaviour," rest home manager Joyce Rodriguez said.
If a resident becomes agitated, they bring them into the room and let them relax, rather than try to medicate them further.
Mrs Rowan said it works "really well" for some people.
"It might not work for everybody but, the ones we have brought in, there's a couple that it's really, really effective," she said.
Mrs Rodriguez said it was easy to get a room full of upset residents if just one became "rarked up", so they would take them into the room to calm them down before the mood spread.
"It sort of goes like a flow-on effect."
Mrs Rowan got the idea from a course she did, and based it on one at Te Awhina, Whanganui Hospital's inpatient acute mental health service.
Mrs Rodriguez said the difference was that Te Awhina's one was filled with "a lot of young boys", whereas "ours has golden oldies".
Residents often spend about 15-20 minutes in it, although some only need a couple of minutes and one woman fell asleep and was there for half an hour.
The room took about a month to set up.